Reliability-based integrated design of steel portal frames with tapered members

Integrated structural designs, with consideration of system reliability for steel portal frames comprising tapered members, are studied in this paper. The reliability-based integrated design (RID) directly checks the structural system limit states and the corresponding system reliability, based on structural nonlinear analysis. The nonlinear integrated analysis model, the semi-analytical simulation method employed for system reliability assessment, the development processes of RID format and the design application of RID formula and curves are presented in this paper. Design examples and comparisons among three different design formats demonstrate that RID proposed in this paper is of certain and consistent system reliability levels, and provides a feasible way for structural engineers to improve the design quality and flexibility of steel frame structures.     

浅谈某高层住宅楼结构设计优化

钢筋混凝土剪力墙高层住宅已成为城市主要建筑结构类型。本文阐述了高层住宅楼结构优化设计的方法和途径,并结合工程实例,进行具体的说明论证。结构设计的优化不是以牺牲建筑结构安全度和抗震性能来求得经济效益的。结构的优化不仅在结构本身,而且涵盖建筑的其他方面,如选择合适的建筑方案,提高建筑空间效率和改善建筑的性价比等。     

Reliability‐based optimum seismic design of RC frames by a metamodel and metaheuristics

The present study is devoted to reliability‐based optimum seismic design (RBOSD) of reinforced concrete (RC) moment frames within the context of performance‐based design. A chaotic enhanced colliding bodies optimization (CECBO) metaheuristic algorithm is proposed to achieve the optimization task. In the framework of CECBO, chaotic maps are employed to achieve randomness that results in better convergence rate in comparison with its standard version. For reliability assessment of structures during the optimization process, the Monte Carlo simulation method is employed. In order to reduce the prohibitive computational burden of the MCS in the optimization setting, a metamodel is proposed to accurately evaluate the required deterministic and probabilistic structural seismic nonlinear responses. Efficiency of the proposed methodology for implementation of RBOSD process for RC frames is illustrated by presenting two numerical examples.     

Benchmark study on reliability estimation in higher dimensions of structural systems – An overview

This work is concerned with a Benchmark study on reliability estimation of structural systems. The Benchmark study attempts to assess various recently proposed alternative procedures for reliability estimation with respect to their accuracy and computational efficiency. The emphasis of this study is on systems which include a large number of random variables. For this purpose three sample problems have been selected which cover a wide range of cases of interest in the engineering practice and involve linear and nonlinear systems with uncertainties in the material properties and/or the loading conditions. Here an overview of the Benchmark study is provided.     

An investigation on the interaction of moment‐resisting frames and shear walls in RC dual systems using endurance time method

Reinforced concrete (RC) dual systems are composed of RC moment‐resisting frames (MRFs) and RC shear walls, where MRFs are barely designed to handle gravity loads. Investigations have demonstrated that shear walls exert negative effects on the upper part of MRFs. In this paper, the interaction of shear walls and MRFs is inspected using endurance time (ET) method. ET is a dynamic time history‐based pushover procedure in which structures are exposed to a set of predefined intensifying ET acceleration functions. In this method, seismic performance of the considered structure is assessed based on earthquake return periods; during which, required predefined seismic performance objectives are fulfilled. In this study, several buildings with RC dual systems were designed based on the conventional codes. Next, their nonlinear duplicates were generated for the application of the ET analysis. It was revealed that shear wall elements impose considerable rotational demands—exceeding the criteria established by ASCE41‐13—on the beams and columns, especially those located on the upper parts of the buildings. This paper puts forth and reviews certain methods to cushion the negative effects brought about by RC shear walls, along with a detailed discussion on their merits and demerits.     

Time-variant finite element reliability analysis – application to the durability of cooling towers

Durability of natural-draught cooling towers is investigated using finite element reliability analysis. A response surface of the linear finite element model is first derived from mechanical considerations. This surface is explicit and exact under certain conditions and requires a single multi-load finite element analysis. This leads to an analytical formulation of the reliability problem. The influence of concrete carbonation and the induced rebars corrosion is then studied in the framework of time-variant reliability analysis. It is shown that the problem reduces to a sequence of time-invariant problems that can be solved using the first-order reliability method (FORM). The evolution in time of the probability of failure in a single point is computed as well as sensitivity factors. Finally, an attempt to introducing space-variant reliability is made. The great difference between the numerical results obtained in the first and in the second approach is emphasized.     

Computational methods for accounting of structural uncertainties, applications to dynamic behavior prediction of piping systems

Computational probabilistic methods enable us to incorporate and propagate uncertainties in mechanical models. However, in some cases, classical methods, such as FORM/SORM methods and Monte-Carlo methods, can be computationally expensive or inaccurate. An efficient importance sampling method is then suggested to yield sufficiently accurate results with acceptable computational cost in an industrial context. The method is an importance sampling method based on a second order asymptotic approximation combined with the HyperCube Latin method. A clustering method is used to solve the global optimization problem which arises to find the points of maximum likelihood. The efficiency of the method compared to classical methods is illustrated with several examples. Considerable reduction of the statistical error of the estimated failure probability can be achieved. The interest of the method is assured provided the points of local maximum likelihood are not too numerous and uniformly distributed. The paper presents two vibratory test cases, the second one is an industrial piping system.     

Optimum design of viscous dissipative links in wall–frame systems

This paper deals with the optimum design of fluid viscous dampers used as dissipative connections in wall–frame structural systems. The analyzed structure is composed of two substructures, the frames and the wall, and it is subject to a seismic acceleration. The optimum design is based on a ‘global protection strategy’, which aims at protecting both the substructures, i.e. both the frame and the wall. In this context, the authors formulate a multi‐objective optimum design, where there are two conflicting objective functions: the displacement of the frame and the shear in the wall. Optimum Pareto solution is obtained. For this purpose, a genetic algorithm, the non‐dominated sorting genetic algorithm II, is adopted. The proposed method uses a global seismic protection strategy: this is a very important issue in modern technical codes, where several performance requirements are fixed and often conflicting. Copyright © 2015 John Wiley & Sons, Ltd.     

Design optimization of truss structures with continuous and discrete variables by hybrid of biogeography‐based optimization and differential evolution methods

This paper presents a hybrid BBO‐DE algorithm by hybridizing biogeography‐based optimization (BBO) and differential evolution (DE) methods for optimum design of truss structures with continuous and discrete variables. In BBO‐DE, the migration operator of BBO method serves as a local exploiter mechanism during the search process. Besides, DE has a role of the global exploration by performing multiple search directions in the search space to preserve more diversity in the population. By embedding of DE algorithm in BBO method as a mutation mechanism, the balance between the exploration and exploitation abilities is further improved. The comparative results with some of the most recently developed methods demonstrate the fast convergence properties of the proposed algorithm and confirm its effectiveness to solve optimum design problems of truss structures with continuous and discrete variables.     

Response of Scots pine (Pinus sylvestris L.) to stress induced by different types of pollutants – testing the fluctuating asymmetry

Damage caused to pine forests by industrial pollution is observed even several decades after emissions have stopped down. A simple morphological feature – the leaf fluctuating asymmetry – was used for assessing the condition of Scots pine (Pinus sylvestris) stands growing in a heavily degraded area. In 2011, a study was performed on the developmental instability of needles in four naturally reforested Polish populations of P. sylvestris. Studies were conducted within the protective zone at a zinc smelter, a copper smelter, a cement plant and train tracks. All selected areas manifested a high extent of anthropogenic pollution‐induced environmental degradation until the end of the 90s. Currently, a reduced level of environmental pollution is recorded at these sites. Control group was a natural population of Scots pine from the region of National Park of Wielkopolska. The results confirm the usefulness of fluctuating asymmetry as a highly sensitive indicator of non‐specific stress. Also, it was shown that in areas degraded by human activity, poor condition of Scots pine persists that the stress factor has been eliminated. This tendency occurs particularly to areas contaminated by heavy metals.